Glass compositions



em like. But- Patented Nov. 30', 1 943 UNITED STATE.

5 PATENT OFFICE GLASS COMPOSITIONS Hans Steinbeck, Dusseldorf-Ge'rresheim, Ger- 7 many; vested in the Alien Property Custodian No Drawing. Application July 12, 1939, Serial No. 284,099. In Germany June 2'1, 193B 5 Claims.

The'invention relates to a moistureand heatresistant glass poor in or substantially free from.

in conjunction with the moisture forms a coating.

or film which continues to attack the glass. Moreover, this coating is electrolytically conductive and deteriorates or destroys metal partsthet may be in contact with it. As the moisture attacks the glass at the surface, the degreeof attack or the amount of lixiviated alkali while depending on thet'emperature and moisture of the surrounding atmosphere is primarily dependent on the specific size of the glasssurface. The

attack is therefore particularly severe with fine properties of glass therefore cannot be fully utilized when the fibers are coated as indicated.

Necessity therefore arose to make such fibers or filaments, especially when to be usedfor electrical insulations or for purposes requiring high thermal and chemical resistance, of glass poor in or free from alkali.

l The known glasses of this kind have the disadvantage that very high temperatures and a long period of time are required to ,melt them, wherefore special furnaces of highly refractory material must be used,. and that their forming glass fibers or filaments which present an enormous specific surface as compared, for example, with thick-walled glass vessels or implements.

Hitherto, there had to be used for technical purposes glass with a certain content of alkali, because the known' glasses free or substantially free from alkali are very difiicult to melt and due to their high softening point also diflicultto form or work. For this reason, one has used the common technical glasses with a more or less high content in alkali also for the production of fibers and filaments. v I

Lately, fine glass fibers and filaments are increasingly used not only for heat'insulations but also for electric insulations. However, in the latter case the insulating power of the fibers is rapidly. reduced or lost when they are exposed a or working temperatures arealso very high. The production and working of these glasses, especially the formation ,of fibers or filaments therefrom is therefore diflicult and expensive.

It is the object of the'pr esentinvention to provide a glass composition poor kali which can be molten without any difilculties atthecommontemperatures of l380 to 1450 C. in ordinary melting furnaces and in the usual period of time and which can be worked, for example drawn to fine fibers or filaments, at temperatures not much higher than the working tem perature of the ordinary commercial glass, and

4 which is highly resistant to heat, moisture and,

' erably than 10 to l5% boric acid, and additions of about chemicals.

1 have discovered that the above properties are inherent in a glass {containing not more than about to silicic acid, no alkali or less than 10% alkali, about 20 to 30% earth alkalies, prefbarium oxide or strontium oxide, not more 3 to 10% alumina, iron oxide and/or ,manzanic oxide and about 2' to. 8% zinc oxide and/or cadmium oxide. In a batch'free from alkali with less than 60% silicic acid, about 20 to earth to the influence of moisture which causes the a 1- kaline surface layers of the. fibers to become elec- 'trolytically conductive. Therefore, it was-necessary to impregnate or coat the fibrous insulations 'or fibers with wster repellent or moisture-resistant substances, such as suitable varnishes and these coatings are much inferior to glass as regards thermal resistance. An im- "presnstedoevarnishggl atmost be heated up to 200' 0., while glass can easilystendtempenturesuptofiw' (Landmo without any glass fiber insulation can alkalies and less than 15% boric acid, suitable proportions for the additions. are 6% alumina, 1

to 5% zinc oxide or cadmium oxide or both vtogether; about 2 to 10% iron oxide or mansanic oxide or both'together, and! to 1% fluorine. I

The use of barium oxide or strontium oxide instead of the ordinarily used calcium. oxide reduces the tendency of the glass to devitrify. The

glass properties in general are furtherimprov'ed. by the saidsddition-ors to 10% o! trivalent oxides. such as alumina, iron oxide [and msngsnic oxide either singly or to eether, and of 2 to 8% or bivalent oxides, such as'sino cad- The fs'voreble therm a oxide elthersinglyor in or free from al- An example of a batch composition'according to the invention for a glass poor in alkali is as follows:

Parts by weight Glass melting sand 365 Borax 225 Feldspar 250 Heavy spar 250' Dolomite 95 Zinc oxide 20 Soda 30 r The glass obtained from this batch has the following composition:

Per cent Bilicic a 53.5 Boric acid 7.5 Alumina Barium oxide 19 Lime 3 Magnesium oxide -a 2 Zinc oxide 2 Alkali oxides 8 v A glass of this kind has a high coefllcient of expansion as compared with the Ordinary Jena.

glass poor in alkali. As a result thereof-fibers" made from this glass will have high mechanical stresses, the favorable infiuence of which on the mechanical and chemical properties of the glass surface is well-known.

As stated above, the alumina can be wholly or partly replaced by iron oxide, manganic oxide or other trivalent oxides, the zinc oxide can be wholly or partly replaced by cadmium oxide and the barium oxide can be wholly or partly replaced The glass obtained from this batch has .the

following composition:

. Variations may be made in the composition within the store-mentioned limits.

This glass possesses the same favorable properties as the glass of the first example. As it is entirely free from alkali it has a particularly high resistance against moisture, steam and other chemical attacks.

Various modifications and variations may be resorted to without departing from the spirit and scope of the present invention appended claims.

Having thus described my invention, what I as defined in the claim as new and desire to secure by Letters Pat out is: a

1. As a product of manufacture, fibrous glass the glass whereof contains 55 to 60% silica, 10 to boric acid, to-% earth alkalies consisting preponderantly of barium oxide, and 3to 10% trivalent oxides selected from the group consisting of alumina, iron oxide and manganese by strontium oxide, lime and magnesium oxide or one or more of these oxides.

The glass is also very resistant against chemical attacks in spite of the low percentage of silicic acid and boric acid. Therefore, only very little alkali can be dissolved even by very moist air, so that fibers or filaments made therefrom lend themselves admirably well for the manufacture of woven or knitted tapes or tubes for electrical insulating purposes. I

Moreover, the tendency of the glass to devitri-v fy is extremely low in spite of the high contents in earth alkali. Also it canbe easily worked or formed in spite of its low content of alkali. Thus, it canbe drawn into finest fibers of any desired length, which are also well suitedfor textile purposes because of their good elastic and mechanicalproperties.

An-example of a batch composition according to the invention for a glass free from alkali is as' follows:

' ,Parts by weight Glass-melting san 550 Hydrated boric. acid 310 Hydrated alumina '15 Dolomite 95 zinc oxide 20 Heavy spar 250 calcined pyrites 20 Manganese ore 10 Calcium fluoride 20 8% cadmium oxide.

' 4. Glass in fibrous form, the

oxide.

2. As a product of manufacture, fibrous glass the glass whereof contains to silicic acid. 10 to 15% boric acid, 20 to 30% earth alkalies consisting preponderantly of barium oxide, 3 to 10% trivalent oxides, and 2 to 8% bivalent, metallic oxides selected from the group consisting of zinc oxide and cadmium oxide.

3. Glass in fibrous form, the glass thereof containing 55 to 60% silicic acid, 10 to 15% boric acid, 20 to 30% of an earth alkali selected from the group consisting of barium oxide and strontium oxide, 3 to 10% trivalent oxides, and 2a;

8% zinc oxide.

taining 55 to, 60% silicic acid, 10 to 15% boric acid, 20 to 30% of an earth alkali selected from th group consisting of barium oxide and strontium oxide, 3 to 10% trivalent oxides, and 2 to I a 5. Glass infibrous form containing 55 to silicic acid, 20 to 30% barium oxide, 10 to 15% boric acid, about 5% alumina, 1 to'5% zinc oxide, and 2 to 10% iron oxide; I Y

' HANS S'I'EINBOCKL glass thereof 0011- 

